Fischer Amps Battery Box 8x Mignon /AA

Stores 8 AA batteries tidily in a neat translucent plastic box, which may be closed with a plastic catch. Markings on the side of each box allow you to separate charged and discharged batteries. Any number of boxes can be stacked horizontally, but I find it a good idea to secure stacked boxes with strips of electrical tape underneath.
Keeping charged cells in these boxes is an excellent way of preventing accidental short circuits.
It is a great pity that the version of this box for AAA batteries is no longer available, although this AA box may also be used to store AAA batteries.

Using lots of those for my field recording gear and stage battery needs. Solid thick plastic box, does exactly what you'd expect - keeps your batteries isolated and safe.